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The purpose of a repeater/frequency coordination entity is to try to keep interference between repeaters and their users to a minimum.
According to Wikipedia, repeater coordination is not required by the Federal Communications Commission (FCC), nor does the FCC regulate, certify, or otherwise regulate frequency coordination.
Amateur Radio Repeater Coordinators or coordination groups are all volunteers and have no legal authority to assume jurisdictional or regional control in any area where the Federal Communications Commission regulates the Amateur Radio Service. The United States Code of Federal Regulations Title 47 CFR, Part 97, which are the laws in which the Amateur Radio Service is regulated clearly states the definition of Frequency Coordinator.
The purpose of coordinating a repeater or frequency is to reduce harmful interference to other fixed operations. Coordinating a repeater or frequency with other fixed operations demonstrates good engineering and amateur practice.